The present invention relates to an epoxy resin composition for encapsulating semiconductors which is excellent in flame retardancy, and to a semiconductor device.
Conventionally, electronic parts such as diodes, transistors and integrated circuits are mainly encapsulated in an epoxy resin composition. This epoxy resin composition contains a bromine compound or a combination of a bromine compound and antimony oxide as a flame retardant, and fused silica or crystalline silica as an inorganic filler. However, from the point of environmental hygiene, flame-retardant resin compositions are demanded which contain neither bromine compounds nor antimony oxide.
For meeting this demand, there has been proposed a red phosphorus-based flame retardant obtained by covering the surface of red phosphorus with a metal hydroxide such as aluminum hydroxide or magnesium hydroxide and further covering the surface of the metal hydroxide with a phenolic resin. However, phosphate ion and phosphite ion eluting from this flame retardant adversely affect moldability and curability of the resin composition and moisture resistance and electric characteristics of the resulting semiconductors, and, thus, none of the resin compositions containing red phosphorus-based flame retardants have satisfied the moldability, the curability, the moisture resistance and the electric characteristics.
For solving the above problems, the present invention provides an epoxy resin composition for encapsulating of semiconductors which is excellent in flame retardancy without containing bromine compounds and antimony oxide by using a red phosphorus-based flame retardant in which total amount of phosphate ion and phosphite ion extracted from the red phosphorus-based retardant is adjusted to less than a certain amount, and provides a semiconductor device made using the resin composition.
The present invention relates to an epoxy resin composition for encapsulating of semiconductors which contains (A) an epoxy resin, (B) a phenolic resin, (C) a curing accelerator, (D) an inorganic filler and (E) a red phosphorus-based flame retardant, wherein the improvement comprises the red phosphorus-based flame retardant (E) having a total content of phosphate ion and phosphite ion eluted from the retardant when subjected to extraction with water at 80xc2x0 C. for 20 hours is not more than 2000 ppm, the amount of the red phosphorus in the red phosphorus-based retardant being 20-40% by weight and the red phosphorus-based retardant being contained in an amount of 0.5-5% by weight in the whole resin composition, and to a semiconductor device manufactured by encapsulating semiconductor elements with said epoxy resin composition.
The epoxy resins used in the present invention include all monomers, oligomers and polymers having two or more epoxy groups in one molecule, and molecular weight and molecular structure thereof are not limited. Examples of the epoxy resins are biphenyl type epoxy resins, bisphenol type epoxy resins, phenolic novolak type epoxy resins, cresol novolak type epoxy resins, triphenolmethane type epoxy resins, alkyl-modified triphenolmethane type epoxy resins and triazine ring-containing epoxy resins. These may be used each alone or in admixture.
The phenolic resins used in the present invention include all monomers, oligomers and polymers having two or more phenolic hydroxyl groups in one molecule, and molecular weight and molecular structure thereof are not limited. Examples of the phenolic resins are phenolic novolak resins, cresol novolak resins, dicyclopentadiene-modified phenolic resins, phenolic aralkyl resins, terpene-modified phenolic resins and triphenolmethane type resins. These may be used each alone or in admixture. As the amount of the phenolic resins, it is preferred that the equivalent ratio of the number of epoxy groups in the epoxy resin and the number of phenolic hydroxyl groups in the phenolic resin is in the range of 0.8-1.2.
The curing accelerators used in the present invention can be those which accelerate the curing reaction of the epoxy group and the phenolic hydroxyl group, and those which are generally used for encapsulating materials can be widely used. Examples thereof are 1,8-diazabicyclo(5,4,0)undecene-7 and 2-methylimidazole. These may be used each alone or in admixture.
The inorganic fillers used in the present invention include, for example, fused silica powder, crystalline silica powder, alumina and silicon nitride, and fused silica powder and crystalline silica powder are preferred. Amount of the inorganic fillers is preferably 70-95% by weight in the whole resin composition from the point of balancing between moldability and reliability. Furthermore, in order to obtain good fluidity and filling properties, the inorganic fillers preferably have an average particle size of 11-20 xcexcm , and such a particle size distribution that those of not more than 10 xcexcm in particle size are present in an amount of 20-45% by weight and those of not less than 70 xcexcm are present in an amount of not more than 10% by weight in the whole resin composition. In a resin composition containing the inorganic filler in a large amount, it is especially preferred to use spherical fused silica powder.
The red phosphorus-based flame retardants used in the present invention are those which have a total content of phosphate ion and phosphite ion eluted from the retardants when subjected to extraction at 80xc2x0 C. for 20 hours is not more than 2000 ppm. In general, red phosphorus alone brings about an oxidation-reduction disproportionation reaction in the presence of moisture when it is left to stand in the air, thereby forming an oxide of phosphorus or an acid on the surface of the red phosphorus particles and simultaneously generating harmful hydrogen phosphide. Since this reaction involves generation of heat, there is the possibility of spontaneous ignition.
Furthermore, in water, red phosphorus causes decrease of pH of water with increase of immersion time to produce an oxide of phosphorus, namely, phosphate ion and phosphite ion, thereby not only causing contamination of the surrounding air with hydrogen phosphide, but also inviting danger of explosion. Moreover, since red phosphorus is highly sensitive to heat or friction and readily ignites and burns at relatively low temperatures or by a slight shock, it always involves dangerousness.
Therefore, red phosphorus is usually covered with a metal hydroxide such as aluminum hydroxide or magnesium hydroxide, and the surface is further covered with a phenolic resin to inhibit contact of red phosphorus with water, whereby oxidation stability of phosphorus is enhanced and, besides, heat resistance and shock resistance are increased. In this case, content of red phosphorus is 80-95% and the metal hydroxide is thinly covered on the outside of red phosphorus. In some cases, only one of the two coverings is made. However, the merely covered red phosphorus is too high in its content and sometimes a part of red phosphorus is exposed due to insufficient covering, and, thus, there is the possibility of ignition owing to a shock. Therefore, in the present invention, a metal hydroxide and a phenolic resin are further added so that the covered red phosphorus has finally a red phosphorus content of 20-40% by weight, namely, there is used a red phosphorus-based flame retardant which is safe against heat and shock.
The contents of phosphate ion and phosphite ion in the red phosphorus-based flame retardant are measured in the following manner. 5 Grams of a sample of the red phosphorus-based flame retardant and 50 grams of pure water are charged in a vessel and treated at 80xc2x0 C. for 20 hours, followed by measuring the amounts of phosphate ion and phosphite ion in the extraction water by ion chromatography.
There are no limitations in the red phosphorus-based retardants as far as the total content of phosphate ion and phosphite ion eluted by the extraction at 80xc2x0 C. for 20 hours is not more than 2000 ppm, but preferred are those in which the red phosphorus content is adjusted to 20-40% by weight by further adding aluminum hydroxide and a phenolic resin to the red phosphorus covered with aluminum hydroxide and phenolic resin.
If the amount of the red phosphorus-based flame retardant in which the total content of phosphate ion and phosphite ion eluted when subjected to the extraction at 80xc2x0 C. for 20 hours is not more than 2000 ppm and the red phosphorus content is 20-40% by weight is less than 0.5% by weight in the whole resin composition, the amount of red phosphorus is insufficient and flame retardancy is insufficient, and if the amount of the red phosphorus-based flame retardant is more than 5.0% by weight, moisture resistance, moldability, curability and electric characteristics of the resin composition are deteriorated. Moreover, when the total content of phosphate ion and phosphite ion eluted when subjected to the extraction at 80xc2x0 C. for 20 hours exceeds 2000 ppm in the red phosphorus-based flame retardant, even if amount of the red phosphorus-based flame retardant is in the range of 0.5-5.0% by weight in the whole resin composition, moisture resistance, moldability, curability and electric characteristics are further deteriorated.
The epoxy resin composition of the present invention preferably comprises (A) 2-20% by weight of the epoxy resin, (B) 2-20% by weight of the phenolic resin, (C) 0.01-1% by weight of the curing accelerator, (D) 70-95% by weight of the inorganic filler and (E) 0.5-5% by weight of the red phosphorus-based flame retardant, with the total amount of these components being 100% by weight, in view of fluidity, curability, and balance between moldability and reliability.
If necessary, the resin composition of the present invention may optionally contain, in addition to the components (A)-(E), a silane coupling agent, a coloring agent such as carbon black or red iron oxide, a releasing agent such as natural wax or synthetic wax, and a low stress additive such as silicone oil or rubber.
The resin composition of the present invention can be made into a molding material by sufficiently uniformly mixing the components (A)-(E) and other additives by a mixer or the like, thereafter melt kneading the mixture by a hot roll, a kneader or the like, cooling the kneaded product and then grinding it. The resulting molding material can be applied to coating, insulation and encapsulating of transistors, integrated circuits and the like which are electrical parts or electronic parts.
For making semiconductor devices by encapsulating electronic parts such as semiconductor elements using the resin composition of the present invention, the composition can be molded and cured by molding methods such as transfer molding, compression molding and injection molding.
By using the epoxy resin compositions for encapsulating of semiconductors of the present invention, there are obtained semiconductor devices containing no bromine compounds and no antimony oxide and excellent in flame retardancy, moisture resistance, moldability, curability and electric characteristics.